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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Dynamic testing of thin-walled composite box beams in a vacuum chamber

Vibration characteristics of thin-walled composite box beams are measured in a rotating environment in a 10-ft diameter vacuum chamber. Symmetric and antisymmetric layup beams are fabricated out of graphite/epoxy prepreg material using an autoclave molding technique. These are excited using piezoelectric ceramic elements and responses are measured using strain gages and accelerometers. First three natural modes are identified using spectrum analyzer over a range of rotational speeds up to 1000 rpm. Measured frequencies and mode shapes (displacement as well as strain) are correlated satisfactorily with calculated finite element results.

Chandra, Ramesh↗
NASA NTRS1990

On-line in-situ control of the resin transfer molding process

Resin transfer molding of three-dimensionally stitched fabrics promises to be a cost effective process for obtaining composite parts of exceptional strength. The technique eliminates many problems involving prepreg preparation, storage and layup. It replaces, on the other hand, the single step cure process with a two-stage impregnation and cure process. Of particular importance therefore is selecting and controlling the viscosity during impregnation and cure. The use of in-situ frequency-dependent electromagnetic sensors and the Loos-Springer model for selecting and controllng the processing properties of the resin transfer molding resin during impregnation and cure are discussed.

Kranbuehl, D.↗
NASA NTRS1991

Apparatus For Chemically Treating Graphite Fibers

New apparatus for chemical treatment of graphite-fiber tow developed. Applies chemical solutions to commercially purchased unsized fibers or in-house-made fibers, to improve following: handling of fibers, interface bonding of fiber to resin matrix during prepreg fabrication, and interface bonding in laminates during molding process. Designed for research and development, with predrying and post-drying in inert environments. Easily adaptable to different chemical solutions and well suited for small-scale, prototype, tailor-made fiber systems. Used to develop fiber/resin composites for aerospace, automotive, marine, and other applications.

Stanfield, Clarence E.↗
NASA NTRS1991

New Polyimide Has Many Uses

Low-toxicity and low-mutogenicity monomer key to new high-performance polyimide. LaRC-IA is thermoplastic polyimide made from 3-4'-oxydianiline and 4,4'-oxydiphthalic anhydride. Good processing characteristics, low toxicity, and no mutagenicity. Adhesives, composite matrix resins, heat resin moldings, and coating films made of new polymer found to exhibit properties identical or superior to commercially available polyimides. Potential applications wide ranging. With and without end capping, employed to prepare unfilled moldings, coatings and free films, adhesive tape, adhesively bonded substrates, prepregs, and composites.

St. Clair, Terry L.↗
NASA NTRS1991

High-toughness graphite/epoxy composite material experiment

The experiment was designed to measure the effect of near-space exposure on mechanical properties of specially toughened 5208/T300 graphite-epoxy composites. The properties measured are elastic modulus, strength, and fracture toughness. Specimens were mounted on an external frame during the time of the LDEF mission. Specimen variables include angle of adjacent plies and fraction of interlaminar contact, which is controlled by the fraction of finely spaced holes in Mylar film placed between the prepreg monolayers of the composite.

Felbeck, David K.↗
NASA NTRS1991

Effects of processing induced defects on laminate response - Interlaminar tensile strength

Four different layup methods were used in the present study of the interlaminar tensile strength of AS4/3501-6 graphite-reinforced epoxy as a function of defects from manufacturing-induced porosity. The methods were: (1) baseline hand layup, (2) solvent wipe of prepreg for resin removal, (3) moisture-introduction between plies, and (4) a low-pressure cure cycle. Pore characterization was conducted according to ASTM D-2734. A significant reduction is noted in the out-of-plane tensile strength as a function of increasing void content; the porosity data were used in an empirical model to predict out-of-plane strength as a function of porosity.

Gurdal, Zafer↗
NASA NTRS1990

Study of flexural rigidity of weavable powder-coated towpreg

An effort has been made to weave powder-impregnated tow into a two-dimensional preform, controlling process variables to obtain high flexural rigidity in the warp direction and greater flexibility in the fill direction. The resulting prepregs have been consolidated into laminates with LaRC-TPI matrices. Complementary SEM and DSC studies have been performed to deepen understanding of the relationship between tow flexibility and heat treatment. Attention is also given to the oven temperature and residence time variables' effects on power/fiber fusion.

Hirt, Douglas E.↗
NASA NTRS1992

Rapid Prototyping Of Layered Composite Parts

Numerically controlled cutting accelerates fabrication of layers. Proposed method derived from stereoscopic lithography. CATIA or CAEDS computer program used to generate three-dimensional mathematical model of prototype part. In model, geometry of part specified in layers, as in stereoscopic lithography. Model data for each layer fed to computer-numerically-controlled ultrasonic cutting machine. Sheet of prepreg (uncured composite material) of specified layer thickness placed in machine and cut, under control of model data, to specified shape of layer.

Wolff, Edwin D.↗
NASA NTRS1991

Squeeze flow and compaction behavior of toughened polyimide matrix composites

The main emphasis was placed upon the squeeze flow and compaction behavior of the Lewis Research Center (LaRC) research project series polyimide matrix composites. The measurement of squeeze film flow behavior was performed by a plastometer which monitors the change of thickness of a prepreg specimen laid between two parallel plates under the specified temperature and pressure history. A critical evaluation of the plastometer data was attempted by examining the morphology of the specimen at various points during the squeeze flow. The effects of crosslinks (Mc) of resin, imidization (B-ataging) condition, and pressure on the squeeze flow behavior were examined. Results are given.

Lee, Byung Lip↗
NASA NTRS1992

Polymer infiltration studies

The preparation is reported of carbon fiber composites using advanced polymer resins. Current and ongoing research activities include: powder towpreg process; weaving, braiding and stitching dry powder prepreg; advanced tow placement; and customized ATP towpreg. The goal of these studies is to produce advanced composite materials for automated part fabrication using textile and robotics technology in the manufacture of subsonic and supersonic aircraft.

Marchello, Joseph M.↗
NASA NTRS1992

Space environmental effects on LDEF composites: Leading graphite/epoxy panel, selected trailing edge specimens

The composite electronics-module cover for the leading edge (row D9) experiment M0003-8 was fabricated from T300 graphite/934 epoxy unidirectional prepreg tape in a multi-oriented layup. This panel contained thermal control coatings in three of the four quadrants with the fourth quadrant left uncoated as a control. The composite experienced different thermal cycling extremes in each quadrant due to the differing optical properties of the coatings. Results will be presented on microcracking and other Low Earth Orbital (LEO) effects on the coated panel substrate.

Dursch, Harry↗
NASA NTRS1991

Flexible thermoset towpregs by electrostatic powder fusion coating

Thermoset prepregs of expoxy and polyimide have been produced by electrostatic deposition of charged fluidized polymer powders on spread continuous fiber tows. The powders are melted onto the fibers by radiant heating to adhere the polymer to the fiber. This process produces towpreg uniformly and rapidly without imposing severe stresses on the fibers. The towpregs produced by this novel process were consolidated to make unidirectional laminates for mechanical testing. Low void content samples have been made and demonstrated by C-scan and scanning electron microscopy. The mechanical properties of unidirectional laminates are equivalent to composites fabricated by conventional techniques.

Yang, Pei-Hua↗
NASA NTRS1992

Improved ablative materials for the ASRM nozzle

Rayon precursor carbon-cloth phenolic was developed more than 30 years ago and is used in most nozzles today including the Poseidon, Trident, Peacekeeper, Small ICBM, Space Shuttle, and numerous tactical and space systems. Specifications and manufacturing controls were placed on these materials and, once qualified, a no-change policy was instituted. The current material is acceptable; however, prepreg variability does not always accommodate the requirements of automation. The advanced solid rocket motor requires material with less variability for automated manufacturing. An advanced solid rocket motor materials team, composed of NASA, Thiokol, Aerojet, SRI, and Lockheed specialists, along with materials suppliers ICI Fiberite/Polycarbon, BP Chemicals/Hitco, and Amoco, embarked on a program to improve the current materials. The program consisted of heat treatment studies and standard and low-density material improvements evaluation. Improvements evaluated included fiber/fabric heat treatments, weave variations, resin application methods, process controls, and monitors.

Canfield, A.↗
NASA NTRS1993

Alternative Cross-Section Towpregs For Robotic Layups

Proposed process suggests robotic placement processing improvements realized by altering cross-sectional shape of wide and flat ribbon materials. Angled cross-section helps composite ribbons to align themselves and correct adjacent tow gaps and overlaps. New prepreg architectures include isosceles triangles, parallelograms, hexagons, and variations of trapezoids.

Baucom, Robert M.↗
NASA NTRS1993

Eddy-Current Monitoring Of Composite Layups

Eddy-current-probe apparatus used to determine predominant orientations of fibers in fiber/matrix composite materials. Apparatus nondestructive, noninvasive means for monitoring composite prepregs and layups during fabrication to ensure predictable and repeatable mechanical properties of finished composite panels. Consists essentially of electromagnet coil wrapped around horseshoe-shaped powdered-iron or ferrite ore. Optionally, capacitor included in series or parallel with coil to form resonant circuit. Impedance monitor excites radio-frequency current in coil and measures impedance of probe circuit. Affected by whatever material placed near ends of core, where material intercepts alternating magnetic field excited in core by current in coil.

Fox, Robert L.↗
NASA NTRS1992

Failure of composite plates under static biaxial planar loading

The project involved detailed investigations into the failure mechanisms in composite plates as a function of hole size (holes centrally located in the plates) under static loading. There were two phases to the project, the first dealing with uniaxial loads along the fiber direction, and the second dealing with coplanar biaxial loading. Results for the uniaxial tests have been reported and published previously, thus this report will place emphasis on the second phase of the project, namely the biaxial tests. The composite plates used in the biaxial loading experiments, as well as the uniaxial, were composed of a single ply unidirectional graphite/epoxy prepreg sandwiched between two layers of transparent thermoplastic. This setup enabled us to examine the failure initiation and propagation modes nondestructively, during the test. Currently, similar tests and analysis of results are in progress for graphite/epoxy cruciform shaped flat laminates. The results obtained from these tests will be available at a later time.

Waas, Anthony M.↗
NASA NTRS1993

Experimental and analytical investigation of dynamic characteristics of extension-twist-coupled composite tubular spars

The results from a study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of extension-twist coupling are presented. A set of extension-twist-coupled composite spars was manufactured with four plies of graphite-epoxy cloth prepreg. These spars were noncircular in cross-section design and were therefore subject to warping deformations. Three different cross-sectional geometries were developed: D-shape, square, and flattened ellipse. Three spars of each type were fabricated to assess the degree of repeatability in the manufacturing process of extension-twist-coupled structures. Results from free-free vibration tests of the spars were compared with results from normal modes and frequency analyses of companion shell-finite-element models. Five global modes were identified within the frequency range from 0 to 2000 Hz for each spar. The experimental results for only one D-shape spar could be determined, however, and agreed within 13.8 percent of the analytical results. Frequencies corresponding to the five global modes for the three square spars agreed within 9.5, 11.6, and 8.5 percent of the respective analytical results and for the three elliptical spars agreed within 4.9, 7.7, and 9.6 percent of the respective analytical results.

Lake, Renee C.↗